The University Experience Dr. Steve Desch Dept. Physics & Astronomy Arizona State University Pathways to College Arizona State University April 22, 2006.

The University ExperienceDr. Steve Desch

Dept. Physics & AstronomyArizona State University

Pathways to College

Arizona State University

April 22, 2006

What do students do at a university?Students learn what has been discovered about the world.

Taking classes. Doing homework. Researching topics.

ASKING QUESTIONS!

Students make new discoveries.

Undergraduates solve assigned problems and sometimes discover something totally new.

Graduate students are expected to discover something new to get Ph.D!

Examples of homework problems

1. Time of sunrise and sunset

2. Emission of radiation from nebulae

Examples of research projects

1. Formation of our Solar System

2. Composition of Pluto’s moon Charon

Outline



north pole

= declination

equator West

South

sunset

= latitude



north pole

= declination

equator West

South

sunset

sunset hour angle

= latitude

cos (Sunset Hour Angle) = - tan() tan()

Declination = 23.44 sin(x),

x = 360 x (# Days since March 21) / 365.25

(Sunset Hour Angle) / 360 = (Time of Sunset) / 24 hours

“Time of Sunset” = number of hours between when Sun is highest in the sky and sunset.

But wait... the Sun is not highest in the sky at noon!



In Phoenix, Sun is highest in the sky at

12:00 + (28.3 + 7.53 cos(x) + 1.5 sin(x) - 9.87 sin(2x) ) minutes

x = 360 x (# Days since March 21) / 365.25



Phx not in middle of time zone

Earth’s orbit around Sun is an ellipse

Earth’s axis tilted relative to its orbit

Students used Excel to solve for times of sunrise and sunset

Jan. 1

June 21

Mar. 20


2. Emission from nebulae



The green light observed in many nebulae is emitted by atoms by the same process at work in neon lights.

In each case, the electrons in the atoms change energy and emit light of very particular wavelengths.

Instead of neon or argon, though, the atoms are doubly ionized oxygen atoms, O+2

Neon atoms

Argon atoms



3P1

3P0

3P2

1D2

1S0

Five lowest energies an electron can have in an O+2 ion

When electrons in O+2 change energy, they emit green light with wavelengths of 4959 and 5007 Angstroms, and blue light with wavelength of 4363 Angstroms 5007 A

4959 A

4363 A



Class assignment was to solve for the rates at which electrons in O+2 change energy levels, and the rates at which O+2 atoms emit light.

Students set up a system of 5 linear equations for 5 unknowns. This has to be solved using linear algebra (matrices).

The students wrote computer programs to solve these equations.

Astrophysicists routinely use the same techniques to determine temperatures and densities of gas in nebulae.

Examples of research problems

1. How did our Solar System form?

Meteorites formed at the birth of the Solar System.

Measurements of different isotopes in meteorites tell us that the early Solar System contained many radioactive elements.

Evidence for one of these, 60Fe, was discovered at ASU in 2003!

Where did it come from?

Tachibana & Huss (2003)



A lot of my research at ASU focuses on showing that it could only have come from a nearby supernova.

But how did our Sun happen to form near a supernova?

Cassiopeia A supernova remnant



The research of one of my ASU colleagues, Jeff Hester, focuses on how stars form.

A lot of them, he finds, form near massive stars, the type that go supernova!



Orion Nebula

protoplanetary disks

~ 1 light-year

HST image, Orion Nebula

Solar Systems are forming right now next to a star that will go supernova in about 1 million years!



ASU graduate student Nic Ouellette is calculating what happens to those new solar systems when a supernova shock hits them.

Results: it is not destroyed! In fact, radioactive elements from the supernova get into the new solar system!!


2. What is Pluto’s moon made of?

Gemini North Observatory, Mauna Kea, Hawaii

Charon & Pluto





ASU graduate student Jason Cook is the first to conclusively identify ammonia in the ice on Charon’s surface!

Ammonia-water mixture melts easily, acts like lava on Europa, Titan, and Enceladus. Maybe Charon, too?

We are currently working toward figuring out whether liquid water could exist under the ice on Charon.

What is the university experience?

Being a witness to discovery. Universities are where many discoveries about the world are made, and students have a front-row seat.

Learning skills. Acquiring the tools needed to analyze the world.

Learning how to learn. University educations are interactive. Asking questions is fundamental. Students learn to take control of their education, and to find the answers to their own questions.

Being an agent of discovery. Every university graduate is expected to master critical thinking, analysis, and the ability to make sense of an otherwise chaotic world.

The University Experience Dr. Steve Desch Dept. Physics & Astronomy Arizona State University Pathways to College Arizona State University April 22, 2006.

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